Studies on the mechanism of action of pneumolysin will be extended using the technique of direct demonstration of cholesterol binding by lysin and the tool of limited proteolysis of the lysin molecule and evaluation of biological activity of the products of proteolysis. Studies on interaction of pneumolysin and granulocytes will be continued and will include assessment of the effect of pneumolysin (and Pseudomonas aeruginosa cytolysin) on chemotoxis, viability, integrity, and metabolism of the leucocytes.